Method for making a yarn and products comprising same

ABSTRACT

A process for manufacturing a continuous yarn, which entails the steps of:a) continously impregnating a mat of mechanically held-together fibers with a mixture of anhydrous size in a liquid state;b) continuosly taking up at least some of the mixture of the anhydrous size by a sizing roller in contact with the mat such that a liquid film having an almost constant thickness of less than 8 mum is formed thereon; andc) depositing the mixture of the anhydrous size, using the sizing roller, on a surface of at least some of a multiplicity of continuous filaments which are formed by mechanical drawing of at least a multiplicity of streams containing molten glass flowing out of orifices of at least one device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of reinforcing fibres and ofcomposites and, in particular, to the deposition of size compositions onglass filaments (or yarns).

2. Description of the Background

The manufacture of reinforcing glass yarns is carried out, in a knownway, starting from streams of molten glass flowing out of the orificesof spinnerets. These streams are drawn in the form of continuousfilaments, and these filaments are then converged into base yarns, whichare then collected.

Before they are converged into the form of yarns, the filaments arecoated with a size by passing over a sizer. This deposition is necessaryfor obtaining the yarns and allows them to be combined with otherorganic and/or inorganic materials in order to produce composites.

The size firstly acts as a lubricant and protects the yarns from theabrasion that results from high-speed friction between the yarns andvarious devices during the aforementioned process.

The size may also, especially after it has cured, provide with theaforementioned yarns integrity, i.e. the mutual bonding of the filamentswithin the yarns. This integrity is especially desired in textileapplications in which the yarns are subjected to high mechanicalstresses. This is because, if the filaments are poorly held together,they break more easily and disrupt the operation of the textilemachinery. What is more, non-integrated yarns are considered to bedifficult to handle.

However, the size is also employed in cases in which this integrity isnot desired, such as in the case of reinforcing fibres, when a high rateof impregnation with the material to be reinforced is desired. Thus, inthe manufacture, for example, of pipes using direct impregnation andfilament winding techniques, open yarns in which the filaments areseparated from one another are used. Small quantities of size,especially less than 0.5% by weight, are then used.

The size also facilitates the wetting and/or impregnation of the yarnsby the materials to be reinforced and helps to create bonds between thesaid yarns and the said materials. The mechanical properties of thecomposites obtained from the material and from the yarns depend inparticular on the quality of the adhesion of the material to the saidyarns and on the ability of the said yarns to be wetted and/orimpregnated by the said material.

Most sizes currently used are aqueous sizes which are simple to handlebut which must be deposited in large quantities on the filaments inorder for them to be effective. Water generally represents more than 90%by weight of these sizes (especially for viscosity reasons), and thismeans that the yarns have to be dried before they are used, it beingpossible for water to impair the good adhesion between the yarns and thematerials to be reinforced. These drying operations are lengthy andexpensive and their effectiveness is not always optimal; they requirethe use of large-capacity ovens. In addition, when they are carried outduring the fibre-forming operation (that is to say before the yarnsobtained by converging the filaments have been collected), either onfilaments (WO 92/05122) or on yarns (U.S Pat. No. 3,853,605), theyrequire the installation of dryers under each spinneret and, when theyare carried out on yarn packages, they run the risk of causing irregularand/or selective migration of the components of the size within thepackages (aqueous sizes already have a tendency to be distributed overthe yarns in an irregular manner because of their nature) and possiblyof causing yarn-coloration or package-distortion phenomena. Moreover,without drying, package distortion is often observed on straight-sidedpackages (rovings) of fine yarns (i.e. yarns having a “count” or “lineardensity” of 300-600 tex (g/km) or less) which are coated with aqueoussizes.

It is to remedy these drawbacks that a novel type of size, which isvirtually free of solvents and called an anhydrous size, has beendeveloped. Anhydrous sizes are curable and/or crosslinkable solutionswhich optionally contain organic solvents and/or water in small amounts,generally of less than 5% by weight. They are distinguishedadvantageously from aqueous sizes by their ability to be distributed ina homogeneous and uniform manner on the surface of the filaments, i.e.forming films of constant thickness, and by the fact that they make anysubsequent drying or solvent-removal treatment unnecessary since thesmall quantities of solvent evaporate during deposition of the size onthe filaments and during curing of the size.

Furthermore, the quantities of anhydrous size deposited on the filamentsare much less than those of aqueous size; thus, when depositing by meansof a sizing roller, a film is formed on the surface of the latter with athickness not exceeding 15 μm in the case of an anhydrous size insteadof a film with a thickness of approximately 90 μm in the case of anaqueous size. Moreover, these small quantities of anhydrous size aredeposited on the filaments with a much higher efficiency, possiblyreaching 100% when the operating conditions are chosen judiciously,whereas this efficiency is generally about 40 to 75% with aqueous sizes.

Anhydrous sizes fall mainly into three categories.

The first category encompasses UV-curable sizes as described in PatentEP 0,570,283 and comprising, for example:

at least one mono-unsaturated or polyunsaturated monomer and/or oligomerof the polyester acrylate, epoxy acrylate, silicone compound or urethaneacrylate type;

at least one photoinitiator, such as benzoin, acetophenone,benzophenone, sulphonylacetophenone and their derivatives, as well asthioxanthones;

if necessary, at least one organic solvent; and, optionally,

additives such as at least a wetting agent, an adhesion promoter, ananti-shrinkage agent, a compatibilizer consisting especially of asilane.

The second family of anhydrous sizes is that of thermally curable and/orcrosslinkable sizes, as described in Patent Applications FR 93/14792 and96/00067.

By way of example, the basic system of these compositions comprises:

an acrylic component and a heat-activated radical-initiating peroxide;or

an epoxy component and an anhydrous constituent which cure by reactingwith each other.

The third category of anhydrous sizes forms part of the teaching ofApplicant FR 97/05926: these are room-temperature curable sizes, thebasic systems of which may contain one or more homopolymerizablemonomers and/or at least two copolymerizable monomers which require noexternal supply of energy. In the case of copolymerization of twomonomers, these may be deposited on the filaments in the form of theirmixture in solution, immediately after this mixture has been formed, orin the form of a first stable solution containing a first monomermixture and of a second stable solution containing a second monomermixture. In the latter variant, the first solution is applied to thefilaments and the second is applied subsequently thereto, at the latestwhile the filaments are being combined into yarns. Be that as it may,the copolymerization generally starts on the filaments as soon as thefirst and second monomers come into contact with each other and, ifnecessary, with the required catalyst or catalysts.

The UV-radiation treatments and heat treatments required to cure thesizes of the two first types mentioned above are carried out in one stepor in several steps, after the filaments have been converged into yarns.Thus, depending on the envisaged use and on the nature of the yarns, anirradiation or heat pretreatment is sometimes carried out at the time ofcollecting the yarns in various forms of packages, in order to precurethe size, the actual curing of which is carried out in a subsequentradiation or heat treatment when the yarn is unwound for the specificapplication for which it is intended, namely a textile application or anapplication of reinforcing organic or inorganic materials. This isbecause the yarn coated with the as yet uncured composition does notexhibit integrity in the ordinary sense of the term since the sheathedfilaments of which the yarn is composed may slip over each other. Thisyarn can therefore be handled easily and, when it is wound in the formof packages, can be easily extracted from the packages without firsthaving to undergo a treatment to cure the size. The yarn coated with theas yet uncured size composition has, moreover, a very high capability ofbeing wetted and impregnated by materials to be reinforced, it thusbeing possible for impregnation to take place more rapidly (increase inproductivity) and the composites obtained thus having a more homogeneousappearance and having certain of their mechanical properties improved.

However, as described in Patent EP-0,570,283, curing the size by the UVirradiation of a yarn in the form of a package may also have advantages.

With regard to depositing anhydrous sizes on glass filaments, severaltechniques are known. Thus, according to Application FR 97/05926 alreadymentioned, this deposition is carried out with the aid of a roller or ofa sprayer, with the aid of a device which also acts as a convergingmeans, or by the use of other yarns or filaments coated with thecomposition and brought into contact with the glass filaments. Thelatter technique makes reference to the special case of producingcomposite yarns, consisting of comingled glass filaments andthermoplastic polymer filaments or yarns.

By definition, deposition by spraying is inevitably accompanied by quitea significant amount of loss of size; the recovery of this lostproportion, assuming that it is possible, constitutes a handicap.

The method of deposition by means of a roller or of a device forconverging the filaments into yarns consists of taking up size from asomewhat viscous and thick liquid film formed on a smooth surface,having ranges of physical properties, especially surface hardness andsurface microporosity, of the type of those of metal surfaces. Startingfrom the observation that the chemical nature of the anhydrous sizesallows them to be used in ever lower quantities, there is currently arequirement for a process for forming an ever thinner liquid film, ofperfectly uniform, controllable and reproducible thickness, on amacroscopicaly smooth surface of the metallic, ceramic or organic type.This is because it may be expected that the take-up of size onto thefilaments from such a film results in the filaments being coated with aminimum quantity of size, with an increased deposition efficiency, i.e.a reduction in the amount of size lost, and for this to be achievedunder completely controlled conditions. Finally, the aim is, of course,to obtain filaments and yarns, and reinforced materials containing them,which have sufficient, or at least preserved, mechanical properties oreven in certain respects novel mechanical properties.

Currently, there is no process making it possible to form, in acontrollable manner, a thin film of anhydrous size at the surface, forexample, of a metal roller. This is because the immersion of the lowerpart of the roller in the size solution coupled with the rotation of theroller results in the formation, at the surface of the roller, of alayer whose characteristics can be controlled only to a small extent byvarying the viscosity of the solution and the rate of rotation of theroller. The thickness of this layer is too great and irregular, and itis impossible to avoid loss of size, in the device for converging thefilaments into yarns or for collecting the yarns, by the size beingthrown off the yarns under the effect of the inherent centrifugal forceat the high winding rates employed.

Moreover, no system for depositing size on a sizing roller with the aidof a metering pump and of an injection nozzle has yet allowed theformation of the desired film.

Furthermore, the previously-mentioned Patent EP 0,570,283 brieflymentions, in its part describing FIG. 1, a coating device 13 consistingof an applicator provided with a felt moistened with a reactive mixtureusing a metering pump. This is because the structure of a felt allows itto soak up a solution in a particularly homogeneous manner. However, thetake-up of size suggested by the European patent, from the felt onto theglass filaments, is not satisfactory in the context of the technicalproblem mentioned above since the deposition of the required smallquantities of size on the filaments could not be achieved except at thecost of the felt drying out somewhat, a situation which, given thenaturally irregular structure of the felt, the surface of which hasfibres of varied dimensions, directions or even textures, would run therisk of the glass filaments catching thereon and therefore the risk ofthe said filaments breaking. Only relatively large amounts of size canthus be deposited in the manner described in the document.

SUMMARY OF THE INVENTION

Consequently, the object of the invention is to provide a process fordepositing, on the surface of glass filaments, minimal quantities ofsize solutions in the form of films of uniform thicknesses and capableof completely coating each filament, in such a way that thesethicknesses can be precisely determined by choosing the operatingconditions appropriately and can be reproduced with satisfactoryreliability.

To this end, the main subject of the invention is a process formanufacturing a continuous yarn, which consists in forming amultiplicity of continuous filaments by the mechanical drawing of amultiplicity of streams of molten thermoplastics flowing out of theorifices of at least one device and which consists in depositing amixture, in the liquid state, on the surface of at least some of thefilaments before they are combined into at least one yarn. The inventionlies more particularly in the successive steps consisting:

in continuously impregnating a mat of mechanically held-together fibres,such as a felt or a woven fabric, with the mixture in the liquid state;

in continuously taking up at least some of the said mixture by means ofa rotating roller in contact with the said mat; and

using the sizing roller, in depositing the said mixture on the filamentswhile they are being drawn.

This process opens the door to the uniform deposition, on the filaments,of quantities of size as low as 0.5 to 1% by weight with respect to theweight of the filaments—quantities which are sufficient in the case,especially, of currently known high-performance anhydrous sizes—with adeposition efficiency close to or equal to 100%.

This efficiency together with the homogeneity and reproducibility of thedeposit formed on the filaments are achieved by virtue of thepossibility, provided by the invention, of forming, on the surface ofthe sizing roller, a liquid film whose thickness is almost constant andless than 8 μm, preferably between 3 and 5 μm, with remarkable precisionand reproducibility.

There is no loss of size to worry about; the gain in productivity isappreciable. For example, in the case of a spinneret producing 800kg/day of filaments, a sizing rate as low as 160 to 350 g/h will besufficient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the most common method of implementation, all the filamentsconstituting the yarn are made of glass. However, the invention does notexclude the variant in which the yarn consists of glass filaments and oforganic filaments, only the glass filaments being provided with acoating of the said mixture in the liquid state or, on the contrary, theorganic filaments also being provided with this coating, or with acoating of a different size, the various size compositions beingespecially capable of reacting with one another. Organic filamentsshould be understood to mean thermoplastic polymer filaments, such aspolypropylene, polyamide or polyester filaments. These polymer filamentsmay be sprayed between the already-sized glass filaments, before allthese filaments are converged into a yarn, as described in Patent EP0,599,695.

Given the abovementioned properties of the anhydrous sizes, as well astheir excellent capability of wetting the filaments, it isunderstandable that the liquid mixture to be deposited on the filamentspreferably consists of such an anhydrous size, for the definition ofwhich reference is made to the contents of the already-mentioned PatentEP 0,570,283 and of the already-mentioned Applications FR 93/14792,96/00067 and FR 97/05926.

Furthermore, a double or multiple application of the process of theinvention to the filaments while they are being drawn, before they areconverged into yarn(s), for the purpose of transferring thereto liquidcompositions capable of reacting with one another especially at ambienttemperature by the copolymerization of constituents belonging to suchseparate compositions, also forms part of the invention. In other words,the overall dimensions of the device necessary for implementing theprocess of the invention in no way prevents two or more of them beingcombined in order to deposit a double coating or a multiple coating on asingle set of filaments, as described in Application FR 97/05926.

The yarns obtained by the process of the invention are generallycollected in the form of packages on rotating supports. The yarnsobtained according to the invention can be easily unwound from thepackages and can be easily handled.

The yarns may also be collected on receiving supports undergoingtranslational motion. They may in fact be sprayed by a device, whichalso serves to draw them, onto the collecting surface which is movingtransversely to the direction of the sprayed filaments, for the purposeof obtaining a web of intermingled continuous yarns, called a “mat”. Theyarns may also be chopped before collecting by a device serving also todraw them.

The yarns obtained according to the invention may thus be in variousforms after collection, especially in the form of reels of continuousfilaments (rovings, cakes, cops, etc.), or in the form of chopped yarns,and may be converged in the form of braids, tapes, mats or networks,these being in woven or non-woven form, etc. The glass filaments formingthese yarns may have a diameter of between 5 and 30 microns and theglass used for producing these filaments may be any glass: E glass, AR(alkali-resistant) glass, etc.

The yarns obtained by a process according to the invention may beadvantageously combined with various materials to be reinforced for thepurpose of producing composite components which have good mechanicalproperties. The composites are advantageously obtained by combining atleast one of the glass yarns according to the invention with at leastone organic and/or inorganic material, the glass content of thesecomposites generally being between 30 and 75% by weight.

Consequently, the subject of the invention is also a product consisting,at least in part, of a yarn obtained by a process as described above.This yarn may or may not have been subjected to a subsequent chopping orweaving treatment, to mechanical spraying or to any other shapingprocess; optionally, it is mixed with an organic or inorganic materialin order to reinforce the latter.

This yarn has a low loss on ignition of at most 3% by weight and even,in many embodiments, at most equal to 1% by weight.

Other features and advantages of the invention will appear in light ofthe following description of the appended drawings in which:

FIGS. 1 to 3 are diagrammatic representations of three devices forimplementing the process of the invention.

These devices comprise a tank 1 of size optionally maintained at aconstant temperature, ensuring that the product is well preserved, so asto guarantee that the metering conditions remain stable.

According to FIG. 1, the size is drawn up by a pump 2 of the peristalticor diaphragm type, which subjects the fluids to particularly low shearstresses.

The quantity drawn up is transferred onto the distributing felt 10 afterhaving passed through a flow meter 3.

In addition, a microcomputer 4 is connected both to the flow meter 3 andto the pump 2 so as permanently to adapt the volume or the mass of sizedelivered by the pump 2 depending on the information supplied by theflow meter.

The devices shown in FIGS. 2 and 3 employ, for feeding the felt 10, acompressed-air supply 5 at the start of the fluid circuit upstream ofthe tank 1.

According to FIG. 2, the size coming from the tank 1 passes through aflow meter 3 and a regulating valve 6, both of these being connected toa microcomputer 4. This time, the microcomputer 4 uses the informationdelivered by the flow meter 3 to control, in real time, any correctionto the flow rate by means of the regulating valve 6.

This regulating function is provided, in the simplified device shown inFIG. 3, by a temperature-compensating volumetric regulating valve 7inserted in the fluid circuit between the pressurized-air supply 5 andthe tank 1. The valve 7, having an integrated and autonomous regulatingfunction, makes it unnecessary to use an auxiliary management andcontrol device of the computer type.

The felt 10 is fixed to a rigid plate, the inclination of which platemay be modified and the pressure exerted on the roller by which platemay be controlled, for example, by means of a controlled-thrustpneumatic cylinder (not shown).

The felt 10 uniformly fed with size, has the function of distributingthe latter over a portion of the surface of the sizing roller 11 whichis slightly larger than that with which the web of filaments 12,delivered by the spinneret 13 and being drawn, comes into contact. Thesize flows into and is distributed in the inclined felt 10 by the actionof gravity. The width of the impregnated area of the felt 10 (i.e. itstransverse dimension with respect to a longitudinal direction defined bythe flow over the inclined plane), the flow time and the distributiontime depend on the viscosity of the size, on the characteristics of thefelt (nature of the constituents, density, texture, dimensions) and onthe positioning geometry (inclination).

The texture of the felt and the viscosity of the size are intimatelyconnected. For example, a dense felt will be wetted on the surface by aviscous size whereas a liquid size will easily penetrate a not verydense felt and will flow out of it without being distributed over itsentire width.

The inclination of the felt also plays an important role in distributingthe size by allowing the gravitational forces to have a greater orlesser effect. This makes it possible to adjust the operation and tocompensate for any shortcomings in the distribution which are due to anot entirely suitable felt.

The optimum correspondence between the viscosity of the size and thedensity of the felt is indicated in the table below in the case of a 30°inclination of the felt with respect to the horizontal, a flow length of6 cm, a distribution width of 6 cm and a cylinder pressure on thecoating device of 1 bar:

Viscosity of the size Density of the felt at 20° C. (cP) (g/dm³) <20200-400  20-50 150-250  50-100 125-175 100-250 100-150 250-400 <100

The nature of the felt has an effect on the quality with which the sizeis distributed in respect of three criteria associated with the type offibre employed: the chemical nature of the fibres, their diameter andtheir homogeneity.

The great majority of the fibres making up the felts are composed ofcellulose fibres or wool fibres. Synthetic fibres are also starting tobe used, such as polypropylene fibres or polyester fibres.

In the case of size compositions whose constituents are not very polar,polypropylene-type synthetic felts are very suitable and the chemicalcompatibility is satisfactory. In the case of compositions having amarked polar character (which is the case with many constituentcomponents in sizes), natural felts, of the wool type (which is morehydrophilic), are preferred.

The chemical compatibility of the various materials of the felts may bemodified in one direction or another by a suitable chemical treatment ofthe fibres. However, the interactions with the components of the size(which, because of their monomeric character, are very good solvents)become difficult to control. In most cases, untreated fibres arepreferred.

In general, the diameter of the fibres must be as homogeneous aspossible in order to make it easier to transfer the size onto theroller. Any heterogeneity in the fibres, in particular the presence ofcoarse fibres, causes localized differences in thickness of the film ofsize on the surface of the sizing roller, but these are neverthelessliable to cause drying-induced breakages at the roller. Fibres of smalldiameter (generally 20 microns) are preferred. In addition, the fibresmust be long enough, flexible enough and sufficiently entangled as toavoid any entrainment of entire fibres or breaks at the surface of theroller. The presence of foreign elements at the surface of the rollergenerally causes breakages whose origin is difficult to determine.

In normal operation, 100% of the size is transferred onto the sizingroller. To achieve such a performance, it is possible to vary differentparameters.

In the first place, the pressure exerted by the felt on the roller leadsto the formation of compressed area within the felt through which theflow is very greatly reduced. However, the pressure must not be too highso as not to damage the roller or the drive mechanisms.

The rotating roller takes up the size available, the latter beingsufficiently compatible with the material of the roller not to cause thephenomenon of dewetting. In addition, the quantity of size is alwaysmuch less than the roller is capable of taking up.

By way of example, in the case of a 40 mm diameter graphite rollerhaving a felt/roller contact length of 80 mm, the pressure that needs tobe exerted is, in most cases, between 0.5 and 3 bar.

Secondly, the speed of rotation of the roller has a certain effect onfelt/roller transfer in a few special cases. Thus, when the size has alow viscosity and the surface of the roller is very effectively wettedthereby (generally, in the case of weakly polar sizes) and/or when thefinal product requires a high loss on ignition, i.e. a large quantity ofsize, it is useful to increase the speed of rotation of the sizingroller in order to increase the take-up area to be wetted and finally toincrease the quantity of size transferred. When a 40 mm diametergraphite roller is used, the rate of rotation of the roller may bevaried between 50 and 150 rpm in order to be satisfactory in most cases.

The third and final parameter to be taken into consideration in thequality of felt/roller transfer is that of the chemical nature and ofthe surface finish of the roller. Moreover, this parameter isincidentally even more significant in respect of the quality ofroller/fibre transfer.

Given that the felt/roller and roller/glass-fibre transfercharacteristics are intimately related, the best material is currentlygraphite.

In normal operation, the technique of depositing anhydrous sizes, asdescribed above, allows a deposition efficiency of very close to orequal to 100% to be achieved. With aqueous sizes, this efficiency isgenerally about 40 to 75%. Given that the cost of the raw materials (interms of dry matter) are substantially equivalent, the economicadvantage of anhydrous sizes deposited using this method is readilyapparent.

In addition, from the environmental standpoint, it is advantageous toeliminate one source of waste which is potentially polluting and givesrise to additional costs in order to destroy the effluents generated.

Should effluent be produced (generally in very small quantity) duringcleaning, testing or operating under special conditions, and given thatall of the waste is of an organic nature, this waste may be easilydestroyed by incineration in suitable plants.

What is claimed is:
 1. A process for manufacturing a continuous yarn,which comprises the steps of: a) continuously impregnating a mat ofmechanically held-together fibers with a mixture of anhydrous size in aliquid state; b) continuously taking up at least some of the mixture ofthe anhydrous size by a sizing roller in contact with the mat such thata liquid film having an almost constant thickness of less than 8 μm isformed thereon; and c) depositing said mixture of the anhydrous size,using the sizing roller, on a surface of at least some of a multiplicityof continuous filaments which are formed by mechanical drawing of amultiplicity of streams comprising molten glass flowing out of orificesof at least one device.
 2. The process of claim 1, wherein themultiplicity of continuous filaments comprise polymer filaments andglass filaments.
 3. The process of claim 1, wherein said mat ofmechanically held-together fibers is a felt or woven fabric.
 4. Theprocess of claim 1, wherein the mixture in the liquid state is ananhydrous size.
 5. The process of claim 1, wherein the mixture forimpregnating the mat is fed by dispensing the mixture from a meteringdevice.
 6. The process of claim 5, wherein the metering device is adiaphragm or peristaltic pump.
 7. The process of claim 1, wherein themetering device comprises a permanent control device comprising a flowmeter inserted into a fluid circuit between the metering device and themat, and a management and control device.
 8. The process of claim 1,wherein the mixture for impregnating the mat is fed by delivering apressurized gas upstream of a tank of the mixture in the liquid state.9. The process of claim 8, wherein the device for feeding the matcomprises a regulating device comprising a flow meter and a regulatingvalve, which are inserted into the fluid circuit between the tank andthe mat, and a management and control device.
 10. The process of claim9, wherein the device for feeding the mat comprises a regulating devicecomprising a temperature-compensating volumetric regulating valveinserted into the fluid circuit between the pressurized-air inlet andthe tank.
 11. The process of claim 1, wherein the surface of the matdefines an inclined plane and the flow and the distribution of themixture in the liquid state within the mat occurs by gravity.
 12. Theprocess of claim 1, wherein the mat comprises synthetic felts, syntheticfabrics, natural felts or natural fabrics.
 13. The process of claim 12,wherein said synthetic felts or synthetic woven fabrics are made ofpolypropylene or polyester.
 14. The process of claim 12, wherein saidnatural felts or natural woven fabrics are made of wool or cellulose.15. The process of claim 1, wherein the mat comprises fibers havingdiameters of less than 20 μm.
 16. The process of claim 1, wherein thesizing roller has surface micropores with dimensions of less than 10 μm.17. The process of claim 1, wherein the sizing roller has a surface madeof graphite.
 18. The process of claim 1, wherein the mixture ofanhydrous size in the liquid state is deposited onto the filaments in anamount of at most 3% by weight with respect to the weight of thefilaments.
 19. The process of claim 1, which is effected several timesin succession in order to transfer, separately, onto the filaments,multiple applications of the mixture of anhydrous size in the liquidstate which react with one another.
 20. The process of claim 19, whereinthe mixture of anhydrous size in the liquid state is deposited on thefilaments in an amount of at most 1% by weight with respect to theweight of the filaments.
 21. The process of claim 1, wherein the mat ofmechanically held-together fibers comprises a web of intermingledcontinuous yarns formed from said filaments.
 22. The process of claim 1,wherein said anhydrous size is selected from the group consisting ofUV-curable sizes, thermally-curable sizes, and room temperature-curablesizes.
 23. The process of claim 2, wherein the thickness of the film ofthe mixture of anhydrous size in the liquid state formed on the surfaceof the sizing roller is between 3 and 5 μm.
 24. The process of claim 1,wherein a deposition efficiency of about 100% is obtained.